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The magmatic system under Hunga volcano before and after the 15 January 2022 eruption - PubMed

  • ️Sun Jan 01 2023

The magmatic system under Hunga volcano before and after the 15 January 2022 eruption

Hélène Le Mével et al. Sci Adv. 2023.

Abstract

One of the largest explosive eruptions instrumentally recorded occurred at Hunga volcano on 15 January 2022. The magma plumbing system under this volcano is unexplored because of inherent difficulties caused by its submarine setting. We use marine gravity data derived from satellite altimetry combined with multibeam bathymetry to model the architecture and dynamics of the magmatic system before and after the January 2022 eruption. We provide geophysical evidence for substantial high-melt content magma accumulation in three reservoirs at shallow depths (2 to 10 kilometers) under the volcano. We estimate that less than ~30% of the existing magma was evacuated by the main eruptive phases, enough to trigger caldera collapse. The eruption and caldera collapse reorganized magma storage, resulting in an increased connectivity between the two spatially distinct reservoirs. Modeling global satellite altimetry-derived gravity data at undersea volcanoes offer a promising reconnaissance tool to probe the subsurface for eruptible magma.

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Figures

Fig. 1.
Fig. 1.. Map of Hunga volcano.

(A) Tectonic setting of the Tofua volcanic arc, part of the Kermadec-Tonga subduction zone. Main volcanoes (red triangles), Hunga volcano (yellow circle), plate boundaries (black lines), and velocities relative to the Australian plate (black arrows, millimeters per year) from the MORVEL model (67). FT, Futuna; NI, Niuafo’ou; TO, Tonga; KE, Kermadec microplates. (B) Pre-2022 multibeam bathymetry of Hunga volcano and topography of the land extent as of September 2017 from (68).

Fig. 2.
Fig. 2.. Pre-, post-, and coeruptive datasets.

(A and B) Marine gravity anomaly derived from satellite altimetry [V31.1 and V32.1, respectively; (21, 23)]. Subaerial island outlines in gray. (C) Change in marine gravity anomaly between (A) and (B). (D and E) Vertical gravity gradient (VGG) data from satellite altimetry [V31.1 and V.32, respectively; (21, 23)]. (F) Change in VGG between (D) and (E). (G) Preeruptive bathymetry, (H) Posteruptive bathymetry (see Materials and Methods), and (I) change in bathymetry between (G) and (H) attributed to the January 2022 Hunga eruption. Caldera outline (green dashed line) and Universal Transverse Mercator (UTM) coordinates (zone 1) tick marks (in kilometers) shown for reference in red.

Fig. 3.
Fig. 3.. Pre-, post-, and coeruptive Bouguer gravity anomalies.

(A) Residual Bouguer gravity anomaly calculated with a crustal density of 2750 kg/m3 and sea water density of 1027 kg/m3, after removing a quadratic polynomial regional trend. (B) Same as (A) but using posteruptive bathymetry and V32.1 of marine gravity anomaly. (C) Change in residual Bouguer gravity anomaly. (D to F) Residual Bouguer gravity anomaly and anomaly change calculated from the VGG data shown in (D), (E), and (F), respectively, and modeled in this paper. Caldera outline (green dashed line) and UTM coordinates (zone 1) tick marks (in kilometers) shown for reference in red.

Fig. 4.
Fig. 4.. 3D density model of the preeruptive magmatic system.

(A) Depth slices and (B and C) cross sections through the density model. Inversion results shown for model norm [0, 2, 2, 2]. Model results for other tested norm combinations are shown in figs. S7 and S8. Color scale shows the density contrast with respect to a reference density of 2.75 g/cm3. Caldera outline (green dashed line) and historical vents (stars). Solid lines are optimal sections through the preeruptive low-density anomalies, and dotted lines are optimal sections through the posteruptive low-density anomalies, to be compared to the posteruptive density model of Fig. 5.

Fig. 5.
Fig. 5.. 3D density model of the posteruptive magmatic system.

(A) Depth slices and (B and C) cross sections through the density model. Inversion results shown for model norm [0, 2, 2, 2]. Model results for other tested norm combinations are shown in figs. S10 and S11. Color scale shows the density contrast with respect to a reference density of 2.75 g/cm3. Caldera outline (green dashed line) and historical vents (stars). Solid lines are optimal sections through the preeruptive low-density anomalies, and dotted lines are optimal sections through the posteruptive low-density anomalies, to be compared to the preeruptive density model of Fig. 4. Orange dashed line is the outline of the two main low-density anomalies for the preeruptive time interval shown on Fig. 4.

Fig. 6.
Fig. 6.. Volume estimates of the main modeled negative density bodies.

Pre-2022 estimates (blue) and post-2022 estimates (yellow) presented for the inversion runs with three different model norm combinations ([1, 2, 2, 2], [1, 1, 1, 1], and [0, 2, 2, 2]) and three different isosurfaces for the central anomaly (A1), northern anomaly (A2), and northwestern anomaly (A3). A1 + A2 represents the volume of the two connected anomalies, after eruption. Green dashed lines in the box plots indicate the samples median, and orange lines indicate the mean. Symbols not contained in the box plots are outliers. Gray squares on the last panel are the sum of the preeruptive median volume values of A1 and A2 anomalies from the three model norms.

Fig. 7.
Fig. 7.. Interpretive model for the Hunga magmatic system evolution.

Proposed architecture and dynamics of the Hunga magmatic system from the gravity models presented in this study. 3D volumes represent isosurfaces of constant density contrasts. Bathymetry (gray surface) is exaggerated vertically 2.4 times, and ash plume is not drawn to scale. Green arrows show the inferred movement of magmatic and/or hydrothermal fluids from one reservoir to another and replenishment from a deeper source. b.s.l., below sea level.

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